4200rpm at 65mph???

[kiwi f150]

Hi Guys i'm hopin someone can help with this problem - i fitted an aftermarket tach and connected it up to the negative side of the coil i also traced and connected it to b6 on the grey socket.
The problem is this: the tach reads twice what the revs are no matter wether its connected to -ve side of coil or tach output in dash - i've checked the back of tach and made sure its on the 8 setting and also tryed all other settings but no go.
has anyone had a similar problem ???
My truck is an 87 F150 5.0 aod .

 

[5.0Flareside]

no... i have a aftermarket tach in my 92 w/351W and it reads perfect... i have to remember how its wired up though...

 

[F 150Cobra]

maybe the tach is damaged i had a tach that readed lower than normal

 

[DNFXDLI]

Sounds like it might be set to read 4 cyl...sometimes there are switches or jumpers that might have to be set.

 

[kiwi f150]

Thanks for the advice guys - i borrowed another tach and fitted that - voila away it goes -new rule for me now:

Rule #1 thou shall not buy cheap c_ _p from the internet.